In nuclear medicine imaging, systems with multiple detectors or detector heads may be used to image a subject. For example, the detectors may be positioned adjacent to the subject to acquire nuclear medicine imaging data (e.g., radioactivity), which is used to generate a three-dimensional (3D) image of the subject. In a specific example, Single Photon Emission Computed Tomography (SPECT) systems may have moving detector heads, such as gamma cameras, positioned to focus on a region of interest. One or more of the gamma cameras may be moved (for example, rotated) to different angular positions to acquire image data. The acquired image data may then be used to generate 3D images.
In single photon imaging systems, such as planar or SPECT imaging systems, collimators may be placed in front of a scintillation crystal or solid state detector to focus the field of view (FOV) of the detectors. The collimators allow gamma rays aligned with the holes of the collimators to pass through to the detector. These detectors need to be calibrated, including during manufacture and periodically after installation, to ensure proper imaging operation. For example, the detectors are calibrated to provide a uniform energy and sensitivity response across the detector units or output channels.
Calibration of these collimated detectors is performed using a calibration emission source that exposes the detectors, and more particularly the entire detector or array of detectors, to radioactive emissions. Accordingly, in pixelated detectors, each pixel is exposed to a statistically relevant number of photons. In some collimated detector systems, calibration with multiple isotopes (having different energy peaks) is not practical after the system is assembled. Accordingly, in collimated detectors, the calibration is performed on the detectors having the collimators removed and using a jig or guide. This enables a two point energy calibration (gain and offset), wherein the calibration uses at least two isotope sources with two different peaks for calibration. Such an approach is time-consuming and difficult, as the detectors must be disassembled and multiple calibrations must be performed.